Mostly I don’t … yes, it is too complicated post, but basically what I wanted to say is that every type of literature has its own spirit, and the spirit of Harry Potter universe is very different in my opinion from the spirit of most fantasy literature. The good crossovers I know about are mostly with the normal stories: crime scene investigation series, spy series, not your average Marvel, StarWars, LotR franchise.

I've been waiting for the day someone writes Aizawa from My Hero Academia beating up Snape. It'd be so cathartic... but yeah, there isn't a whole lot outsides of the MOD!Harry fics that crossover with BNHA, but it-s good fun.

Pretty decent LoTR one. Shadow of Angmar. Started a little rough but improved over the course. It’s since been abandoned but overall I enjoyed reading it.

https://m.fanfiction.net/s/11115934/1/The-Shadow-of-Angmar

No, I’ve never found them engaging.